Filters: Variance

Posted by on Nov 16, 2006; 7:50am
URL: http://imagej.273.s1.nabble.com/Filters-Variance-tp3700988.html

Hello,

Here one question about Process/Filter/Variance. I am trying to
understand what is behind the Variance filter. I make a text image with
the following matrix:

1 1 1
1 2 1
1 1 1

Then I run Variance filter on the image, with radiue = 2. The I got an
image with all 9 pixel value = 0.95238.

My understanding is that it would take a 3x3 matrix, calculate variance
of the 9 elements (which is 0.1111), then put it back to the center
position of the 3x3 matrix, without changing value of the elements at
the edge, i.e.
1 1 1
1 0.11 1
1 1 1
       
Is my understanding correct? Could anybody tell me how ImageJ calculate
this Variance filter?

Any comments will be appreciated.

ZQ